The present invention relates to a navigation instrument for use with road way vehicles such as rally cars, autobuses and trucks operated on a regular run, etc.
Navigation instrument have been incorporated in road way vehicle for calculating and displaying vehicle running conditions with respect to scheduled ones so that the driver can arrive at the destination on time.
For better understanding of the navigation instrument, its principle will be described in more detail.
Assuming now that T denotes a running time, X a running distance, and Vs a running average vehicle speed, following relation is obtained: EQU T=X/Vs
From the above equation, the running deviation distance .DELTA.X and the running deviation time .DELTA.T are calculated with the following equations: EQU .DELTA.T=T-X/Vs (1) EQU .DELTA.X=.DELTA.T.times.Vs (2)
These data showing the running distance/time deviations are displayed on the display unit associated with the navigation instrument.
FIG. 1 shows a graph schematically illustrating an example of variation of the actual running speed with respect to the average running vehicle speed Vs. As understood from FIG. 1, if the actual running speed maintained so that its value is equal to the running average vehicle velocity Vs independent of passing of time, the running distance X will increases with a linear relationship.
However, as shown in FIG. 1, the actual running speed varies with respect to the average running speed Vs. Accordingly, e.g. at a time T=T.sub.1, the running deviation distance and the running deviation time are expressed as .DELTA.X.sub.1, and .DELTA.T.sub.1, respectively, as taught by equations (1) and (2).
Referring to FIG. 2, there is illustrated in more detail one embodiment of the conventional navigation instrument. The distance detector 10 includes a pulse generator 12 for providing a pulse every time the vehicle travels a constant distance and a first counter 14 for counting the pulse fed thereto from the pulse generator 12. The time detector 20 includes a clock pulse generator 22 including a crystal oscillator and a second counter 20 for counting the clock pulses fed thereto from the clock pulse generator 22. A scheduled speed setting unit 30 is provided for use in setting a scheduled average speed. A set switch 40 is provided for use in loading or writing the average vehicle speed set by the setting unit 30 to a first memory (which will be described soon). The outputs of the distance detector 10, the time detector 20, the speed setting unit 30 and the set switch 40 are coupled to an arithmetic unit 100. The arithmetic unit 100 comprises a first divider 51 for dividing the output (travelling distance X) from the first counter 14 by the output (travelling time T) from the second counter 24 to provide a vehicle average speed V, a second divider 52 for dividing the output (travelling distance X) from the first counter 14 by the output (average running speed Vs) of the memory 42, a subtractor 53 for subtracting the output of the second divider 52 from the output of the second counter 24 to provide a travelling time deviation .DELTA.T=T-X/Vs, and a multiplier 54 for multipling the output Vs of the memory 42 by the output (.DELTA.=T-X/Vs) of the subtractor 53 to provide a travelling distance deviation .DELTA.X=.DELTA.T.times.Vs.
Reference numeral 60 denotes a signal selector means responsive to a data selector command from the arithmetic means 100, and sequentially outputting one of the three data signals V, .DELTA.X, and .DELTA.T from the arithmetic means 100.
In more detail, the signal selector means 60 comprises a multiplexor 62 and a selecting circuit 64 producing a data select signal f in accordance with the data selector command. The multiplexor 62 sequentially outputs one of the three data signals V, .DELTA.X, and .DELTA.T fed thereto as parallel inputs in accordance with the data select signal f.
Reference numeral 70 denotes a display unit 70 such as comprised of 7-segment digit indicator. The display unit 70 indicates the contents represented by the signal fed from the signal selector means 60.
In operation, before the vehicle stars, the set switch 40 is switched on. Thus, the first counter 14 and the second counter 24 are resetted. At the same time, the data showing the average running vehicle velocity set by the setting unit 30 is stored in the memory 42. When the vehicle starts, the first counter 14 counts pulses produced every time the vehicle advances for a constant distance, and producing an output signal showing the running distance X of the vehicle from a starting point. The second counter 24 counts the time reference pulses produced at a constant interval, and producing an output signal showing the running time of the vehicle from a starting point. These outputs X and T of the first and second counters are fed to the first divider 51. Thus, a data showing an average time X/Vs is obtained. This average time data X/Vs and the time data T are applied to the subtractor 53. Thus, the running deviation time .DELTA.T=T-X/Vs is obtained. On the other hand, the output .DELTA.T of the subtractor 53 and the running average vehicle velocity Vs from the memory 42 are fed to the multiplier 54. Thus, a data .DELTA.X=.DELTA.T.multidot.Vs showing a running deviation distance is obtained as an output of the multiplier 54.
These data V, .DELTA.T and .DELTA.X are fed to the multiplexer 62. The multiplexor 62 selectively supplies each data V, .DELTA.T and .DELTA.X to the display unit 70 in accordance with the data select signal f of the selecting circuit 64. Thus, these data V, .DELTA.T and .DELTA.X are displayed on the display unit 70.
It is here noted that the arithmetic means 100 and the signal selector means 60 may be composed by digital or analogue circuit.
However, with the conventional navigation instrument, when the average running vehicle veloity is newly set, the stored information in the first and second counters 14 and 24 is cleared by the set operation of the set switch 40. As a result, the data showing the running deviation distance .DELTA.T and the running deviation time .DELTA.T at the time lapse when the average running vehicle velocity is altered.
For instance, at a rally race, it is required that the driver drives the vehicle so that the vehicle runs at a corresponding designated speed over a plurality of designated speed section. In such a case, with the conventional navigation instrument, it is necessary for the driver to take a note of the data showing the running deviation distance and the running time every running section. When the driver wants to find the accumulated deviation data at the present time, it is necessary for the driver to calculate the accumulated deviation data on the basis of each data described in the note and the data indicated on the display unit. These manual calculation for the accumulated deviation data will be considerably troublesome for the driver.